Litter boxes used for animals such as cats are known.
For example, the patent literature 1 discloses an animal litter box having a longitudinal direction, a transverse direction and a vertical direction and including three parts, i.e., a lower container placed on the lower side, an upper side cover put on an upper end of the lower container and a cover put on the upper side cover.
The upper side cover includes a bottom wall through which liquid passes and which extends on the lower side thereof and cooperates with the lower container to define a receiving space in such a manner that liquid inflows into this space.
The lower container includes an excrement tray adapted to be movable in the longitudinal direction between a put-in position within the receiving space below the bottom wall of the upper side cover and a position outside the receiving space. This tray has a rectangular bottom wall in its planar view and side wall rising from a peripheral edge defined by four sides of the bottom wall.